1. Field of the Invention
The invention relates generally to polymeric coupling agents and a method for making the same. More particularly, this invention relates to a polycarbonate-silane polymer made from a reaction between polycarbonate and 3-glycidoxypropyltrimethoxysilane (GPS) in the presence of a catalyst, preferably a quaternary ammonium salt.
2. Prior Art
Polycarbonates are well known engineering thermoplastics having high performance characteristics. Polycarbonates are tough, rigid, dimensionally stable and have outstanding impact strength. It will be appreciated that polycarbonate polymers are widely used as glazing materials because of their clarity and toughness. Unfortunately, such optically clear sheets and other articles of polycarbonate can be rather easily scratched and marred. This problem may be overcome by applying a protective coating over the polycarbonate made from a harder, more mar resistant material such as a siliceous abrasion-resistant coating. It would be particularly advantageous to effect a strong chemical bond between the siliceous coating and the polycabonate substrate.
Major manufacturers have been marketing polycarbonate coated with cured silica-filled polysiloxane compositions which are adhered to the polycarbonate substrate through the use of various primers. Examples of polysiloxanes utilized can be found in U.S. Pat. No. 3,451,838; U.S. Pat. No. 4,022,855 and U.S. Pat. No. 4,207,357, among others. Some of these include primers patented in U.S. Pat. No. 3,707,397, U.S. Pat. No. 4,210,699, JP 01-149,878 and UP 03-6,282. These are all reasonably effective but fail to completely alleviate the problems associated with the debonding of the coating composition from the polycarbonate substrate, particularly where moisture and repeated thermal cycling are environmental factors.
Silane coupling agents have also been investigated but have not proved acceptable, particularly in moist and hot environments. The introduction of normal silane coupling agent of either a solution of functional organoalkoxysilane or its hydrolysate into the interface between the polycarbonate and the coating has not proved successful because of insufficient interactions between the coupling agent and the substrate. The result is that eyeglasses, windows, sport lenses, in-roadway reflectors, etc. often appear to debond over a period of time.
Epoxy has also been used to coat polycarbonate with various epoxide primers. Some examples of these are found in U.S. Pat. Nos. 4,747,725; 3,098,056; 3,220,974; 3,261,808 and 3,258,356. These similarly have had only measurable success. Therefore, there still is a strong need for a way to coat polycarbonate reliably and which exhibits better durability.